Editor's Summary
24 August 2006
Oxygen or what?
The amount of oxygen in the Earth's atmosphere is thought to have increased dramatically about 2.4 billion years ago. The strongest evidence for this increase is the presence of a chemical signature known as mass-independently fractionated sulphur isotopes (MIF-S) in rocks older than that, and its absence in younger rocks. The MIF-S signature is well established as a marker for low atmospheric oxygen levels, but a report in this issue gives pause for thought. Some rocks that formed before 2.4 billion years ago appear not to contain MIF-S. This suggests either that atmospheric oxygen levels fluctuated dramatically before 2.4 billion years ago, or that MIF-S is not the reliable indicator of low oxygen levels that is has been assumed to be.
News and Views: Earth Sciences: Signature required
Most geologists agree that Earth's atmosphere was oxygen-free until 2.4 billion years ago. But the latest sulphur-isotope measurements from sedimentary rocks suggest otherwise.
L. Paul Knauth
doi:10.1038/442873a
Letter: Sulphur isotope evidence for an oxic Archaean atmosphere
Hiroshi Ohmoto, Yumiko Watanabe, Hiroaki Ikemi, Simon R. Poulson and Bruce E. Taylor
doi:10.1038/nature05044
First paragraph | Full Text | PDF (381K) | Supplementary information
